U.S. Pat. No. 3,954,611 describes a method and a portable apparatus for purifying lubrication oil for machinery such as gearboxes and pump unit motors for oil wells.
Patent GB 2202460 describes an installation for the cleaning of a unit which via a pump creates the circulation of oil which passes through some filters to retain the impurities.
The patent application Ser. No. WO0153723 describes a method and a system for checking the cleanliness of the gear units used in gas turbines on aeroplanes, in which the oil that goes through the gear unit is pumped and later guided to a filter, after which the filter is removed to determine the weight of the collected particles which are then compared with the predetermined levels for the correct functioning of the gear units.
The patent application US20040035805 describes a method and an apparatus for the cleaning of various types of machine pollutants that includes hoses that connect to the machine, a pump that circulate the liquid and a low capacity filter for vaporising the fluid. It also has an automatic ventilation system which injects air into the fluid at determined time intervals.
None of the equipment described in the documents mentioned efficiently resolve the problem posed in the case of clean oil for gearboxes used in wind turbines during the hours of operation.